Batteries or electrochemical cells are commonly used electrical energy sources. A battery contains a negative electrode, typically called the anode, and a positive electrode, typically called the cathode. The anode contains an active material that can be oxidized; the cathode contains or consumes an active material that can be reduced. The anode active material is capable of reducing the cathode active material.
When a battery is used as an electrical energy source in a device, electrical contact is made to the anode and the cathode, allowing electrons to flow through the device and permitting the respective oxidation and reduction reactions to occur to provide electrical power. An electrolyte in contact with the anode and the cathode contains ions that flow through the separator between the electrodes to maintain charge balance throughout the battery during discharge.
One type of battery includes an alkali metal as the anode active material and iron disulfide as the cathode active material. The battery can be a primary battery. Primary batteries are meant to be discharged (e.g., to exhaustion) only once, and then discarded. In other words, primary batteries are not intended to be recharged. Primary batteries are described, for example, in David Linden, Handbook of Batteries (McGraw-Hill, 2d ed. 1995). In contrast, secondary batteries can be recharged for many times (e.g., more than fifty times, more than a hundred times, or more). In some cases, secondary batteries can include relatively robust separators, such as those having many layers and/or that are relatively thick. Secondary batteries can also be designed to accommodate for changes, such as swelling, that can occur in the batteries. Secondary batteries are described, for example, in Falk & Salkind, “Alkaline Storage Batteries”, John Wiley & Sons, Inc. 1969, and DeVirloy et al., U.S. Pat. No. 345,124.